Aug 032014
The sun rises higher in the sky in summer, and travels around more of it, than in winter.

The sun rises higher in the sky in summer, and travels around more of it, than in winter.

Many of the preferred locations for prepper retreats are in areas that have substantial swings in temperatures between hot summers (daytime temperatures often in the 90s and sometimes exceeding 100) and cold winters (where temperatures seldom rise above freezing, even in the middle of the day).

That’s no big deal when you have unlimited utility power for heating and cooling, limited only by your ability to pay the electricity or gas bill each month.  But in a Level 2 or 3 situation, there won’t be any utility power, and creating our own electricity will be expensive and always in short supply.

We need to make our retreat structures as energy efficient as possible so as to minimize the need for heating and cooling.

There are lots of ways to improve the energy efficiency of our retreats, and most of these are totally ignored in ‘normal’ building design and construction because it makes little financial sense to, for example, spend an extra $50,000 when building your retreat, and to get a $500 a year saving in energy consumption as a result.  But in a Level 2/3 situation, the cost of the energy might rise from $500 to $5000 or more, and/or it might simply not be available at any cost, and so the financial equation changes drastically, making it more prudent for us to invest up front in additional energy-saving techniques in order to enjoy the benefits if/when we need to rely on our retreat and make do with less energy.

The good news is that not all these strategies need to be expensive or inconvenient, and some of them actually add to the livability of your retreat.  One such example is adding what in various forms can be considered either an awning, a brise soleil, a shade or a veranda (verandah – both spellings seem acceptable) to your retreat’s southerly (and much lesserly, east and west-facing) aspect.  (We’re not explaining what an awning, shade or veranda is because you probably know, but the term brise soleil might be less familiar.)

The clever aspect of such structures is that they interact with and take advantage of the way the sun rises in the sky.  In the summer, the sun quickly climbs up to a near vertical position before descending again at the end of the day.  In the winter, the sun slowly staggers part-way up the sky before sinking down again.  This difference is also more exaggerated, the further you move from the equator, and most of us are planning our retreats to be far from the equator.


Note – as shown above – the sun rises a bit north of east and sets a bit north of west in the summer, but in the winter it rises south of east and sets south of west.

It covers more of the sky in summer, and you might notice appreciable sun coming in from west and east facing windows, and possibly even a little bit in northern windows too.  But it is the southern facing windows that most need the sun shading.


What this means – and as illustrated above – is that some sort of shading/blocking structure that prevents the sun’s rays from shining onto and into our retreat while the sun is high in the sky will reduce solar heating during the summer – the time of year when we most want to keep the sun off our retreat and out of our windows.  But during the winter, when we’re keen to get all the sunlight and warmth we can, the overhead structure won’t interfere with the sun’s rays at all.  Heads we win, tails we don’t lose!

Because these devices take advantage of the varying seasonal location of the sun, they can be fixed in position, making them potentially robust and low maintenance.

How much sun angle should they block?  One approach is to see the maximum angle in the sky for the sun in mid-winter, the angle at the equinoxes, and block off all angles greater than the equinoxes.  You can get this information from this helpful website – simply put in your location and then choose 21 December as the date, and that tells you the maximum height the sun reaches at your location in the winter.

For example, in Kalispell MT (48º12′ north) the sun struggles to reach 18.4º up into the sky.  Compare that to the summer solstice (21 June) when it reaches 65.2º.  At the equinoxes (21 March and September) the sun goes up to 42.2º – a number which unsurprisingly is sort of halfway between the two other numbers.

One other interesting thing is to note that the sun has risen to 42.2º in mid summer by 10.10am and doesn’t fall below it again until 5.10pm.

So perhaps it makes sense to accept something around the 42.2º point as the transition from when we want to allow sun into the house and when we want to block it.  That gives us full sun for half the year, and successively blocks off more of the sun during the summer season.

This calculation should be modified by an appreciation of what type of heating/cooling needs you’ll have at the equinoxes.  Will you still be wanting to heat the retreat, or will you be starting to need to cool it?  That will also influence how much shade cover you want above your windows.


Having some type of permanent shade over your southerly facing windows is a simple way of ‘automatically’ regulating and cutting down on the sun’s heat that transfers inside your retreat during the summer while not reducing it during the winter.

It is probably the most cost-effective thing to do in terms of improving your retreat’s energy efficiency and reducing its need for cooling during the summer.  Be sure to include shading if designing a new retreat, and be sure to add it if purchasing an existing dwelling structure.

May 152014
In theory, the 55 panels on this roof might be capable of providing up to 14 kW of power.  But, in reality?  Probably closer to 10 kW.

In theory, the 55 panels on this roof might be capable of providing up to 14 kW of power. But, in reality? Probably closer to 10 kW.

So there you are, thinking about buying some solar panels.  You’ve noticed they come in a range of semi-standard shapes and sizes, and maybe you’ve even noticed that the slightly unusual dimensions (such as 39.4″) actually make sense if converted to metrics (ie 39.4″ = 1 meter).

You also notice all sorts of acronyms floating around in the specifications and warranties, and you sort of wonder if, when comparing the power output of Brand X’s 250 watt panel with that of Brand Y’s 255 watt panel, if there truly is 5 watts of difference, and, for that matter, whether either panel will ever produce close to the claimed 250 watt output, and what that actually means in terms of total kWhrs a day.

Perhaps even worse are advertisements with no acronyms or qualifiers at all, just a list of unexplained specifications.  Who is making those claims, and how credible are they?

These are all good questions.  We’ll try to answer them for you.

The good news is that there are some official standards that can apply to how solar panel power outputs are measured.  The not so good news is that while these official standards might provide a level playing field for how to measure one panel’s power output alongside another panel, the results obtained by the standards do not necessarily match the real world experience you’ll get (a bit like how the official mpg figures for new cars are seldom the same as you get yourself in real-world driving).  But first, let’s understand exactly what solar panels give you, and why it so quickly becomes difficult to establish their true power output.

All solar panels provide their power in DC volts and amps.  The actual power they provide (which is measured in watts) is calculated by multiplying their output voltage by the amps of current that flows at that voltage – this might seem like a simple calculation, but it isn’t – the voltage level varies based on the amps that are flowing, and both also vary based on the intensity of the sunlight falling on the panel.  So even a simple seeming power measurement isn’t quite as simple as it should be.

It gets worse.  When you start connecting a series of panels together, the real world practical power you might get is not necessarily the simple sum of the power outputs of each individual panel.

However, simple or not, a DC watt specification is the most direct measure of their power output.  Occasionally you may see panels with an AC wattage rating – these would be panels with individual ‘micro-inverters’ that convert the DC output of the panel immediately to AC, right at the panel.

At least until recently, it has been most common to connect together the DC output from multiple panels, then feed that combined power to a single central inverter that then converts it to AC.  But there are convincing studies to suggest that micro-inverters are a very good thing, and while they might slightly add to the cost of a solar array installation, they might also result in you getting appreciably more power out of the system in real life, as compared to the implied power outputs quoted by the specifications.

For now, simply be aware that all inverters involve a slight and inevitable power loss (typically an inverter is anywhere from 95% to 98% efficient) and so if you are seeing an AC watt rating, this has already had the inverter power loss removed.  For example, a 250W DC panel, after passing through a 96% efficient inverter, would end up giving you 240W of AC power.

In other words, AC watts are generally ‘better’ than DC watts, when comparing numbers.

Now for some official ‘standards’ for solar cell power measurements, and note that usually power measurements are made by the manufacturer, rather than by an independent third-party, so there is a certain amount of trust required when accepting these numbers, no matter what the standard may be that they are claimed to have been measured by.

Many cells are rated based on a STC rating.  STC stands for ‘Standard Test Conditions’.  These are an ambient temperature of 25°C/77°F, sunlight of a 1000 W/sq m intensity falling directly on the panel, an air mass of 1.5, and zero wind speed.

Another rating is the NOCT rating.  This is the Normal Operating Cell Temperature rating, and it will always give a lower rating.  NOCT ratings assume 800 W/sq m of solar power falling on the cell, a 20°C/68°F ambient temperature, and a wind of 1 m/sec (2.24 mph) blowing on the backside of the solar panel for cooling.

Even this is optimistic.  The way most solar panels are laid out prevents any underneath cooling, and so their temperatures can rise appreciably, and as they get hotter, they become less efficient (once the air temperature gets up into the high 80s, you’re probably going to start losing 1% of power for every two degrees F of temperature rise).

But wait – there’s more.  Would you be surprised to learn that California does its own thing?  It uses a different standard, the PTC standard.  Unlike the STC rating, the PTC rating is not a measured rating, but a theoretical rating.  That might seem like a backwards step, but it is based on adjusted realworld data, and unlike the self-assessed STC rating, the PTC rating, at least as expressed by California’s CEC (California Energy Commission) requires independent lab results rather than accepting manufacturer claims.

PTC stands for Photovoltaics for Utility Systems Applications Test Conditions, in case you wondered.

Here is an interesting table of PTC ratings for solar panels.  If you go down the list, you’ll see that sometimes panels with a manufacturer stated lower power capacity than another panel actually test as giving more power, and you’ll see appreciable differences between panels all offering apparently the same output.

So maybe you can decide that your 250 W panel actually produces 225 watts to start with.

But then, you need to start adjusting further down.  Perhaps the panel was slightly under specs when it came from the manufacturer.  It will probably lose almost 1% of its output each year that it is operational – do you want to plan your system based on its best case output when brand new, or its mid-life output when it is 5, 10, even 20 years old?

The allow for inverter losses, additional losses through its wiring, and some shading/uneven lighting losses (both from clouds as well as from things like trees around your site).  Add a bit more for other miscellaneous electrical losses, and some for dirt on the panels, and all of a sudden, that 250W panel is starting to promise you more like 150 watts of real power.

One of the subtle but potential huge power losses is from shading.  Now you sort of understand that if the sunlight halves in ‘strength’, then so too does the power output of your panels halve.  But did you know that a partial bit of shading, on only perhaps 10% of your panel, can reduce its output by 50%?  That’s an amazing but observably true issue.  There’s a good discussion about that issue here.

There’s another related factor to keep in the back of your mind as well.  Not all the power your panels will create is necessarily generically usable power.  For example, let’s say you have 2kWh of power produced in a day – that seems like a meaningful chunk of power.  But that doesn’t mean you can run a 1500 watt appliance for over an hour, because perhaps the power is trickling in at only 300W, over a seven hour period.

You’ll never be able to run your 1500 watt appliance from the 2kW of power you got that day, unless you feel the power into a battery bank over the day and then take it all out at the 1500 watt rate – oh yes, and if you do that, you’ll then have to factor in the additional inefficiencies of converting from the AC power to DC power for the battery charger, then the loss in charging up the battery, then the loss in discharging the battery, and the loss in converting the battery DC power back to AC power for your appliance.


So, your 250 watt panel will probably never ever give you 250 watts of power, under any conditions.  We’d suggest that you use the Californian PTC test results to convert your panels’ claimed power outputs into more realistic output levels, and then reduce those by at least 10% to convert from panel power output in DC to actual AC power available in your home.  In other words, expect less than 200 watts – in best case conditions – from your 250 watt panels, and in worst case conditions (but still with nice sunny weather) you could be dropping down closer to 150 watts as your theoretical maximum.

The bottom line for us as preppers, and remembering we are planning for a future where solar panels aren’t just a fashionably nice ‘green’ supplement to our normal power from the utility company, but rather are our only power source, is this :  Massively over-build your solar array, because no matter how big it is/becomes, it will disappoint and leave you wanting more when you actually start living off the power.

This is a further part of our series on solar energy.  Please also visit our sections on energy in general and solar energy in particular for more related articles.

May 142014
Which is more energy efficient to boil water?  This $10 plastic electric jug, or a $500 microwave oven?  The answer might surprise you!

Which is more energy-efficient to boil water? This $10 plastic electric jug, or a $500 microwave oven? The answer might surprise you!

We recommended either buying or making your own ‘Wonderbag’ type product and using it for an energy-efficient type of slow-cooking yesterday.  But what about cooking items when a slow-cook approach is not practical or possible?  For example, what is the best way of boiling water?

If you want to boil water, you probably have various choices – you can boil a kettle (or a pot) on a stove top element, you might have an electric jug, you could use an oven, or a microwave oven.

Now it goes without saying that using a regular oven would be a very slow and inappropriate process, but what about the difference between, eg, stove top, an electric jug, and the microwave?

We were able to exactly test the difference between an electric jug and a microwave oven, and we can empirically comment on the stove top as another alternative.

For our testing, we used a microwave oven that had a nameplate power rating of 1560 watts, and an electric jug with a nameplate power rating of 1500 watts.  We heated one liter of water in a glass container in the microwave, and one liter of water in the electric jug itself.  The electric jug did not have an immersion exposed element, but rather had a smooth base and the element directly below it.

We observed a rise of 34.9°C by the water in the jug, and 19.1°C by the water in the microwave during the two-minute period.  We also noted that the water in the jug was slowly continuing to rise at the end of the heating period – this was to be expected because the very hot electric element had some thermal inertia and was continuing to transfer energy after it was switched off.

So, a quick result is that there was almost twice as much net heating from the jug as from the microwave, even though the microwave was drawing slightly more power.  That would seem to argue conclusively in favor of using the jug rather than the microwave.

We were interested to know exactly how efficient each process was, so we did the calculation to compare the electrical energy consumed and the thermal energy created.

Two minutes of the jug at 1500 watts represents 50 watt hours of power.  Two minutes of the microwave at 1560 watts is 52 watt hours of power.

Increasing the temperature of 1L of water by 34.9 degrees requires 40.52 watt hours of energy.  So, for the jug, we got 40.52 watt hours of heat from 50 watts of electricity, which is an 81% efficiency rating.

For the microwave, the 19.1 degree temperature rise required 22.18 watt hours of energy, and we used 52 watt hours to create that.  This represents a 43% efficiency.

Clearly, the jug is much better than the microwave for heating water.

Where Did the Rest of the Energy Go?

You might be wondering what happened to the rest of the energy.  In the case of the jug, the balance of the energy was probably radiated away from the jug – heat from the sides of the jug, and more heat from its spout at the top.  An 81% efficiency rating is actually a reasonably good result.

The microwave’s much greater energy loss requires a bit more explanation.  First, we have the efficiency (or perhaps we should say, the inefficiency) of converting electricity to microwave energy.  This is generally thought to involve about a 40% loss of energy.  So, of the 52 watt hours that went into the microwave unit, 20.8 of them got ‘lost’ in the electronics.  More power was spent to spin the turntable, to illuminate the light, and to operate the fan (although these three things are all moderately low power drains).

Not all the microwave energy inside the cavity (and of the 52 watts, probably less than 30 watts actually ended up as microwaves) was absorbed by the water.  In addition, just like the heat that was lost out of the top of the electric jug, the open beaker we had the water contained within definitely was allowing heat to escape from the top.  If we had some sort of lid to put on the beaker, that would have probably made a measurable improvement.

So, the observed efficiencies are in line with the theoretical estimates of energy losses.

The Best Electric Jug?

If you don’t yet have an electric jug, we’d suggest you consider a plastic one, because the plastic will give you better insulation and have less heat loss through the jug sides than is the case with a pretty nice looking stainless steel one.

Our favorite jug (which is not the one we tested with) is this Proctor unit.  It is the one pictured at the top of the article.

It is plastic, it has a small minimum fill requirement, it has a fully exposed element for best heat transfer, and – wow – it is only $9 at Amazon.  What a deal that is.

Hidden Microwave Advantages

On the face of it, you’d think there’s never a reason to use a microwave oven instead of a jug when you want to boil water, right?

Well, actually, wrong.  If you are boiling a jug, you need to put a minimum amount of water in it, no matter how much water you need to heat up.  Indeed, our test jug suggests a 1.3L minimum fill (but note the Proctor unit is happy with only 300 mls).

With the microwave, you only need to put a single cup of water in it, if you are only needing to heat a single cup of water (a cup of coffee requires maybe 400 mls, depending on how large a cup you want).  In such cases, this may compensate for the microwave’s lower efficiency.

Stovetop Cooking Considerations

Okay, so that sort of explains the relativity of microwave ovens to electric jugs.

But what about boiling water on the stove top?  That is a bit harder to establish without special test equipment and digging in to the stove’s wiring or gas pipes to accurately measure energy consumption, and it also varies from case to case depending on the efficiency of the heat transfer from the heat source to the heat recipient (such things as the size and shape of the pot bottom, the size and shape of the element/burner, etc), the pot material (glass, aluminium, copper, steel, etc) and so on.  Two different scenarios could give you two massively different results, with one twice as good/bad as the other.

However, there have been some studies done which have clear and interesting results, and if we assume reasonably optimized setups, we can make some generalizations.

The least efficient form of heating is invariably gas.  You are lucky to get about a 35% – 40% efficiency from a gas burner on a stove – that is, for every three units of gas energy, you get one unit of heat transferred into your pot.

Regular smooth flat electric elements are rated as about 70% – 75% efficient, and induction cookers are about 80% – 85% efficient.

Another source claims 55% efficiency for gas, 65% efficiency for regular electric, and 90% efficiency for induction cooking.  As we said, a lot depends on the specific setup you’re using.  While the numbers are different, the relativity is the same.  Gas is the least efficient, regular electric in the middle, and induction way in the front.

In particular, if you have gas, make sure the flames do not spill over the sides of the pot.  That’s totally wasted heat.  Any time you see the water boiling first around the side of your pot, you know you are wasting gas heat and should turn down the gas.

For electric cooking, make sure the pot bottom sits flat on the element surface, and is clean.  Dirt acts as an insulation barrier, and if there are air gaps, then you are heating the air rather than the pot.

Induction Elements

Normally, when electricity is abundant and relatively inexpensive, no-one cares about the greater energy efficiency of an induction cooktop, and you have to be more specific about the types of pots you use with an induction cooktop, too.  Many of us also prefer the greater control of gas compared to traditional electric elements, and although gas is less efficient, it is also usually cheaper, per unit of energy, to use gas rather than electricity, so the efficiency issue is sort of cancelled out by the cost saving.

But WTSHTF and all energy becomes scarce and costly, it becomes very beneficial to consider an induction cooker.  There are other benefits to induction cooking, too – it is a bit like gas because it too can instantly increase or decrease the energy being applied to your pot, with no ‘thermal lag’ as is the case with regular electricity.  It can also do clever things like detect if your pot has boiled dry or not.

The good news is you don’t need to go out and buy a whole new stove top right now.  You can simply buy a single free-standing induction cooker.  Amazon has them for about $60 – $100, they are available elsewhere too of course.

We see some model induction cooktops are rated at 1300 watts and others at 1800 watts.  While you might instinctively go for the 1800 watt unit, there’s a potential small problem there.  1800 watts on 120 volts requires 15 amps of current.  So make sure you run it off a 20A rated circuit, and make sure you don’t share the circuit with anything else that consumes much power, or else you’ll trip the circuit breaker.

Needless to say, practice with the induction cooker, so you know its quirks and how to get best (and most energy-efficient) use from it.  And make sure you have the appropriate pots to go with it too – ideally pots the same diameter as the induction heating circuit.

Oven Cooking

An oven can be either an efficient or an inefficient means of cooking.  It is efficient if you are cooking large amounts of food for a long time; it is inefficient if you are heating up leftovers the next day.

You can sense this without needing to measure, just by doing a thought experiment.  Say you turn your oven on and heat it up to 350 degrees, then when it is hot, you put something in and cook it for 45 minutes.

How long does it take to heat the oven to 350°?  Probably about 15 minutes, maybe longer.  So there is 15 minutes with the oven elements on full, all the time.  Your oven probably has 3 kW – 5kW of heating elements; let’s average and say it has a 4 kW heater inside.  You’ve used 1 kWh of energy just to heat up the oven prior to cooking in it.  If you have a daily energy budget of 10 kWh, you’ve used 10% of it just to heat up your oven.  Ouch!

If you then have it cooking for a while, the oven is probably only cycling the heating elements on for 25% of the time or thereabouts, so for 45 minutes of heating, you might use another 0.75 kWh of energy.  So 45 minutes of cooking uses 1.75kWh of energy total, but if you were cooking something for more than twice as long, eg, two hours, you’d use much less than twice as much energy (ie 3 kWh for two hours of cooking).  The oven becomes more efficient, the longer it is cooking something.

The other issue to do with oven efficiency is how much food you have in it.  Most of the energy in an oven goes to keeping the air in the oven hot, and the heat transfer to the food is slow and inefficient.  It costs little more to cook ten pounds of meat or whatever in your oven than it does to cook 10 ounces of meat or whatever.

So, an electric oven is good for large quantities of food cooked for a long time, but it is bad – very bad – for a small quantity of food cooked for a short time.

Let’s come back to the ‘heating leftovers’ example.  Maybe you heat your oven to 350° then heat the item for 30 minutes.  That’s 1.5 kWh of energy.  Compare that to perhaps 6 minutes in the microwave, which would be 0.15 kWh – ten times less energy.  That makes for an obvious choice, doesn’t it!


There are several things we can conclude from all of this.

1.  If heating the same amount of water, an electric jug with immersion water heater is the most efficient way to do this.

2.  If heating less than half the minimum amount of water you’d need to heat in a jug, use a microwave oven.

3.  If cooking on the stove-top, induction elements are the best, and gas elements are by far the worst.

4.  Traditional ovens work best when cooking large amounts of food for a long time.  For small amounts of food, that only need a short time in the oven, it is usually better to use a microwave oven instead.

As preppers, we suggest you ensure you have three cooking appliances as part of your kit.  An electric jug, an induction cooktop, and a microwave oven.

May 132014
You can never save too much energy when planning for life after TEOTWAWKI.

The Wonderbag – something you can also easily make yourself – gives you a low energy way to make a high quality meal.

You can never save too much energy when planning for life after TEOTWAWKI.

But there is more to saving energy than shivering in the cold, in the dark, in your retreat.  We need to rethink the underlying assumptions that are embodied in many of the everyday things in our lives – things that have been designed for maximum convenience and in the belief that energy will remain freely abundant and wonderfully inexpensive.

Trust us – even at 15c or more per kWh of electricity, that is truly ‘wonderfully inexpensive’ compared to what energy will cost you (or be valued at) when you have to make your own.

One of the greater consumers of energy in your house is your kitchen.  Many of the appliances in your kitchen are enormously wasteful of energy.  Think, for example, of your toaster – an efficient toaster would have a radiant element (the same as your normal toaster) but mounted horizontally, and then with the bread placed above it, so that the rising heat hits the bread, rather than goes out the top of the toaster.  We’ve not timed our typical pop-up toaster, but we’ll guess it takes maybe 3 or 4 minutes to toast two slices of bread, and at maybe 1500 watts, that’s about 0.1 kWh of energy for two slices of toast.  If you are setting yourself a total daily energy budget of, say, 10 kWh, you’ve used 1% of it just on your morning toast.

Add another 1% or more to boil water for your morning coffee (the chances are your jug requires you to boil a certain minimum amount of water, most of which is unnecessarily heated if all you want is a cup’s worth of water for a cup of coffee.  Modern jugs are nice and convenient, but are also not as efficient as old-fashioned jugs with an element that is immersed in the water it is heating, causing more/most (heck, pretty much all) of the heat to be transferred to the water it is heating.

Now look at your stove top.  Maybe you are cooking a meal, and you’re boiling potatoes in water for 20 minutes.  Every steam bubble that comes out of the water in the pot is wasted energy.  Potatoes will cook as fast at 211°F – right before the water starts sucking up more energy to boil – as they will at 212°F, and please don’t be like the people who think that food cooks faster in water that has a ‘rolling boil’ with lots of steam being given off, as compared to water that is gently simmering right around the boiling point.

The only reason we cook things in boiling water is because it is easy to control the temperature of boiling water, and makes for predictable cooking times.  How, in a typical kitchen, could you maintain water at a different temperature such as, eg, 210°F instead of at 212°F?

One more thing about boiling.  Did you know it takes five and a half times more energy to boil a given quantity of water (ie to take water at 100°C/212°F and change it to steam at the same temperature) than it does to raise the temperature of that water from 0°C/32°F (ie water right at freezing point but not frozen) to 100°C/212°F.  Converting water to steam requires huge amounts of energy, all of which is being unnecessarily wasted in your pot of boiling water, which would cook your food just as well at 99°C/211°F as it does at 100°C/212°F.

(If you want the actual numbers, it requires 333 J/gm to melt ice, 4.18 J/gm to heat water each degree C, and 2,230 J/gm to convert water to steam at boiling point.  As an interesting aside, this is the underlying principle of how a steam engine works – some of the energy that is absorbed when water becomes steam is then recovered when the steam drives the pistons and condenses back to water again.  The steam is merely another way of transferring and converting the thermal energy of the fire to the kinetic energy from the piston/cylinder.)

One more thing about boiling water in your jug.  Turn the jug off just before the water reaches the boil, and use that water.  You’ll save a measurable amount of energy.  Indeed, the ideal temperature for coffee is about 200°F, and a bit cooler for tea.

Your pot of potatoes isn’t just losing energy through unnecessarily boiling.  Feel the sides of the pot, and its lid too.  Feel around the bottom of the pot where the burner or hot plate/element is.  But be careful, because it is all very hot – and all that heat that you feel, and which is being dissipated away from the cooking food, that is all wasted energy.  About the only good thing that can be said for that wasted energy is that it is helping to heat your kitchen (but that’s actually a bad thing on a hot summer’s day – you then need to turn around and use more energy to run your a/c to take the heat out of the house!).

Now, you probably also have some sort of slow cooker/crockpot in your kitchen cupboards, too.  This confirms the fact that you don’t need to cook food fast (at 100°C/212°F) in order to cook it well, indeed some people say that slow cooked food ends up much better than fast cooked food.  Your slow cooker can be used for meats, vegetables, soups, stews, pretty much most things.  If you are like us, you probably seldom use yours, and in our case, we simultaneously love and hate the ‘slow torture’ of the tantalizing smells that come from it all day during the cooking process.

We are not suggesting you can save energy by using the typical crockpot/slow cooker that you probably have in your kitchen.  At least with the ones we’ve seen, it is still heating the liquid around the edges to beyond boiling, and the overall construction is not well insulated.

A Low Energy Slow Cooking Solution

What we are saying is that these concepts can be combined to create a ‘do it yourself’ low energy slow cooking device that will save you a great deal of energy.  In its simplest form, put whatever you want to cook into a regular pot, heat it up to boiling, then hold it right at about boiling until such time as the food has absorbed the first rush of heat energy from the water, then at that point, take it off the stove and wrap it up in insulation, then leave it to slowly continue cooking for however long it takes.  All the heat in the pot goes into cooking the food, rather than being wasted away.

This will take longer for a meal to be prepared, but it will also use much less energy.  And the time it takes is not personal time you need to spend standing watching, but simply elapsed time while the food ‘does its own thing’, slowly cooking away.  Prepare your evening meal at lunchtime, then come back and eat it at dinner time.

One approach to this concept can be seen in the ‘Wonderbag’.  Although designed and marketed as a device to variously ‘save the planet’ and suchlike, all the benefits they talk about on this page of their website apply with only very little change in context, to what our lives may be like in a Level 2 or 3 scenario.

The Wonderbag itself seems to be nothing more than quite a lot of foam insulation inside a fabric bag that envelopes your pot to keep the heat in the pot, cooking the food, after you’ve originally heated it up.  They sell the bags on Amazon for $50 a piece, which strikes us as expensive, but we’re told we should feel good about paying over the odds for the Wonderbag because we’re helping to save the planet in the process – as you see on their webpage, the more Wonderbags we buy, the fewer the rapes of women in Africa that will occur!

There are plenty of recipes on their site as well, and most slow cooker recipes can be used with little change (possibly slightly longer cooking times because the average temperature will drop down once you insulate the pot off the stove).

Note also some essential safety issues – don’t let the temperature drop below 140°F because if you do that, you’re entering the ‘sweet zone’ where bacteria thrive.  We’d be tempted to stick a remote temperature probe in the pot to monitor the temperature.  There are also some helpful questions and answers on the Amazon product page about how best to optimize your cooking style and pot selection, etc, when using a Wonderbag or any other similar product you create yourself.

How much energy would Wonderbag type cooking save you each day?  The Wonderbag site claims that ‘fuel and water usage extended by 60% or more’ so that seems like you are at least halving the energy required to cook a meal.  How much energy is that?  Hard to say, but coming back to the 20 minutes of boiling potatoes, plus 5 minutes to boil some other vegetable, and however many minutes to somehow cook some meat, it seems to us that you’re probably saving more than 0.5 kWh, but probably not more than 1.0 kWh, per meal you cook via an insulated cooker.  That’s not much when electricity costs you about 10c – 15c per kWh, but in the future, when energy is precious and scarce, this amount of energy saving becomes significant when you’re trying to live within a 10kWh or less a day energy budget.

Best of all, it doesn’t require you to turn down the heat and turn off the lights!  Instead, it gives you lovely flavorful tender and nutritious food.

Note :  Please see, also, our article ‘What is the Most Efficient Form of Cooking‘ for further discussion on the best ways to cook your food when energy is scarce and costly.

May 122014
Let our spreadsheet save you the need to employ a team of clerks to calculate your solar energy situation.

Let our spreadsheet save you the need to employ a team of clerks to calculate your solar energy situation.

One of the most important things for you to get right is balancing your retreat’s energy requirements with its energy production and storage.

These three variables – how much energy you use, how much you produce, and how much you store – are all dependent on each other, in a complex series of interlinked relationships, and all you really know for sure is that you never want to run out!

But trying to match together the theoretical output of your solar panels, adjusting for changing weather and sunshine during the year, and adding in some energy storage capacity (batteries or whatever) to tide you over the times when your solar power isn’t producing (every night and much of every day during the winter, too) is a confusing and difficult process, and it just becomes harder still when you try to answer such questions as ‘should I add more panels or more batteries’.  Oh yes, and you’ll also want to know the costs of each different way of designing your system too.

In truth, it is hard to avoid getting out a big piece of paper, a pencil or two, some erasers, and a calculator, then devoting hours to running through the specifics of this.  But we can help you to get very close to knowing the answers to these questions without having to spend too much time or hassle doing so.

We’ve programmed up an Excel spreadsheet that allows you to simply enter in the information related to your retreat and your planned power generating, storage, and consumption numbers.  Then it will instantly do literally thousands of calculations and tell you if your scenario will work or not, and show you where the energy shortfalls will be, and allow you to then try ‘what if’ scenarios such as ‘what if I add another panel’ and ‘what if I add another battery’ to get as close as possible to the point where you can confidently predict you’ll never run out of power, no matter how bad the weather.

Of course, once you’ve worked through the spreadsheet, we suggest you then do the ‘real thing’ and calculate the exact specifics for yourself, but at least the spreadsheet will zero you in on the critical parameters and so you only need to confirm the spreadsheet, rather than start from scratch.

We have a link to the spreadsheet for you to download (and we’ve even filled it with some typical values for Coeur d’Alene so you’ve got a reference point to start from) and some pages of explanatory notes to help you know what to fill in and how to interpret the results, all starting from this page here.

This is the first time we’ve created a spreadsheet for you to work forward from.  Do you like it?  Is it helpful?  Would you like more (and, if so, please give us suggestions).

Note – while we are proud of the spreadsheet and consider it very helpful indeed, it is not perfect.  Please be sure to understand its limitations, which we list also on the linked page.  If the spreadsheet proves popular, we’ll improve the sophistication of the model in the future.

Oh yes, if it all gets too much like rocket science, we can help, over and above the large book sized amount of information we’ve already published on the site!  We are happy to consult with you and do most of this on your behalf, and to walk you through the personal preference/lifestyle choices that we can’t make for you.  Rates for our energy consulting services are reasonable and start at $250.  Let us know if we can assist.

May 102014
Chances are you'll end up choosing to cover most, if not all your roof with solar panels.

Chances are you’ll end up choosing to cover most, if not all your roof with solar panels.

This is a further part of our series on solar energy.  Please also visit our sections on energy in general and solar energy in particular for more related articles.

What makes a roof better or less suited for having solar panels mounted on it?  How should you design a new retreat structure, and/or, if looking at buying an existing dwelling, how do you know if it is optimized for solar?

Answering these questions is reasonably straightforward.  To start with, if you are looking at buying an existing retreat structure, it absolutely must have a southerly facing roof and an unobstructed view of the southern sky from directly south to about 75° either side of directly south.  You don’t need a full 180° of clearance, but anything much less than 75° either side of south means you’ll start losing some morning or evening sun.

Ideally the roof should have a fairly steep pitch on it.  The ideal angle for solar panels is to have them angled at the same number of degrees as the latitude the panels are at.  That means, if you’re in a northern state, you probably want to have a 45° angle, or even possibly slightly more.  If you think of a line between the two Portlands, the one in Oregon is at 45.5° N and the one in Maine is at 43.7° N, that gives you an intuitive feeling for your likely latitude, and remember that much of the Canadian border follows the 49th parallel, ie, 49° N.  To be more exact, you can instantly see any latitude anywhere from Google Earth and other mapping programs.

It is acceptable to have a somewhat flatter pitch (or a steeper pitch, but that’s less likely!), but once your pitch starts to be more than perhaps 15° away from your latitude, you’re going to start to feel a loss in solar energy production.  A 15° differential will cost you 3.5%, and the loss of power starts to quickly rise from that point forward.

If you are going to build your own retreat, choose a lot that will allow you to build with this southerly aspect, and design your roof for as close to your ideal pitch as is practical.  One thing is likely – you’ll be getting a lot of attic space that way!

Indeed, if you don’t have height restrictions, rather than having a typical ridge line roof with two equal roof sides rising to meet in the middle, why not consider a single sloping roof, going all the way up to the top.  This would give you a lot of extra space above your top level in your structure, and while this space would be facing to the north rather than south, it could surely be used for just about any normal purpose.

How Much Roof Area Do You Need?

Now, the next question becomes either ‘how much roof area do you need’ (if you’re designing a new dwelling) or ‘how much power can you get from the roof you have’ (if you’re buying an existing retreat structure.

The answer to both questions is very much ‘it depends’.  But there are some simple rules of thumb you can use.

At present, it seems that a typical solar panel measures about 39.13″ x 65.04″, and typically generates about 250W according to its official specification sheet.  Some panels will give you fewer watts for this panel size, and some higher priced ones will go up to 275W for the same size.

The panel is close to 18.35 sq ft in size.  So, divide 250W by 18.35 sq ft, and here’s a rule of thumb :  Ideally, with reasonably efficient solar cells in the panels, you can get about 13.5 watts of solar power per square foot of roof area.  If you make adjustments to allow for not every square inch of roof space being usable, and leaving some maintenance walkway space and such like, we’d probably suggest that for quick guesstimate calculations, you figure on 11 watts per square foot of roof.

A 250W panel, which seems to be about the sweet spot for price vs performance, will cost about $250 (plus the associated costs for wiring, installation, control systems, and so on).  This points to another rule of thumb – figure about $1 per watt of panel capacity, plus more to install, etc, the panels and power from them.

Remember that your total roof area will be greater than the footprint of your dwelling.  The slope means it has more length on it, and there is probably some overhang that adds to the roof dimensions too.  But remember also to deduct any parts of the roof that aren’t southerly facing – the ‘other side’ of a typical two-sided roof, the ‘hip’ sides of a hipped roof, and so on.  Also, if there are corners and sides to your roof, possibly the sides might shade the main south-facing roof portion, potentially almost halving the power production on areas that would be shaded.

You probably have a target amount of power generating capacity you would like for your retreat (see our article on ‘How Much Solar Power Generating Capacity Do You Need‘ for more discussion on this).  Multiply your roof square footage by 11, to see an approximate maximum generating capacity for your roof.  Is that above, below, or close to your target capacity?

If your roof clearly has more than enough space for the generating capacity you need/want, then you can relax, and proceed with all the other things to consider when evaluating current retreats or planning your own custom retreat.

If your roof is marginally close to meeting your power requirements, maybe you should calculate things more carefully.  In this case, we suggest the easiest thing to do is to get scissors and paper.  Cut out a large shape that represents the portion of your roof that is southerly facing.  Then cut out, to the same scale, the number of 250W panels you want to place on your roof (maybe, to make things quicker/easier, cut out larger shapes that represent strips of 2, 3, 4 panels).

Lay the panel shapes out on the roof shape.  Leave some aisles for you to walk along (or up and down) so that you can access your roof for maintenance (hopefully seldom) and cleaning (depending on where you live, cleaning will be a reasonably regular activity).  We suggest you allow about 2ft wide corridors, and you design things so you’re readily able to reach panels with a ‘window washing’ type extendable handled cleaning device (which indeed might be a window washer).  Maybe you can plan to reach out 9′ or so from where you are standing.  So that would allow for aisles every 18′ if you access the panels from both sides, and perhaps you’d want the first aisle 9′ from the edge of the roof.

We don’t know why, but we see very few roof installations that leave aisles to make it easy to access the panels, but we feel this to be essential.  It doesn’t take much dust or dirt or leaves or branches or bird poo or whatever to massively reduce a panel’s power output, so we believe regular panel cleaning is essential.  Perhaps the designs with no walk-ways assume that you’ll do the cleaning from a ladder or from the other side of the roof, and those are both possible options.  But if you’re like us, the easier something is to do, the more likely you are to do it, and so we’re keen to make this as easy as possible for us.

So, lay out the panels as best you can and see how many will fit.  The good news is the panels can be laid in either direction – long side horizontal (ie ‘landscape’) or long side vertical (ie ‘portrait’).  While it mightn’t look so nice aesthetically, you can even have a mix of different orientations, any way that will allow for best space utilization.

Measuring Roof Slope and True Roof Surface Area

If you can conveniently climb onto your roof and safely walk around on it, then the easiest thing to do is measure it directly.

But if this is not so practical, you’ll need to measure what you can on the ground and then adjust based on the roof slope for the actual roof surface area.

There are two typical ways of measuring roof slope.  One – less common in the US – is to talk about the angle of the roof slope.  The other is to talk about the slope in terms of units of vertical rise per so many units of horizontal run.

You probably know – or can easily measure – the horizontal length of the building footprint, and you also can probably measure the vertical rise.  It is also possible to measure the degrees of inclination with only some relatively simple tools, but for most of us it will be easier to measure the horizontal length and rise.

Let’s look at a worked example.  Say you have a roof that has a 30 foot ‘footprint’ – ie, it covers 30 ft of horizontal level floor.  It has a single ridge in the middle, and the rise from either end to the middle is 6 feet.

If you remember way back to your trigonometry days, you might remember Pythagoras’ Theorem for finding the length of the third side of a triangle.  The sum of the squares of the other two sides equals the square of the hypotenuse, right?  And in the case of your roof, you now know the two sides around the right angle (ie 6 feet for the rise and 15 ft for the horizontal length).  So

62 + 152 = 36 + 225 = 261, and √261 = 16.2

The roof length is 16.2 ft – not much more than the length on the ground in the case of what would be a fairly moderate slope on the roof.

Oh, and for the sake of completeness, if you do know the angle of the roof and the horizontal length to the ridge point, then you can calculate the roof length by the formula

Roof length = Horizontal length divided by the cosine of the angle.

For example, a roof with a 30 degree pitch and a 15 foot horizontal length to its ridge would have a length of

15/cos(30°) = 15/0.866 = 17.4 ft.

A Sample Calculation

Say you have a 1250 sq ft building footprint (perhaps 25′ x 50′).  Say you extend your roof one foot over this footprint for eaves/overhang (generally it is common to have greater overhang).  And you give the roof a 45° degree pitch.

Of course, you want the long side of the house to be facing south.

If you have a standard single ridged roof, with no hips, and if the roof is in equal halves about the central ridge, then the actual dimensions for each half will be 52′ long (the 50′ width plus an extra foot at each end) and the width will be 37.4′ (the 25 ft flat length becomes a 35.4 ft length on a 45° angle, plus an extra foot of overhang at each end).  But remember that only half of this is facing the sun, so in total, you have 972 sq ft of roof area facing the sun.

Now let’s allow for some maintenance aisles.  Should these lanes run along the roof, or up and down it?  We’re not sure which is better, you can decide.  But let’s simply, for now, set aside 20% of the gross area to leave you room for these aisles.  So your 972 sq ft of panel area has a net usable area of 778 sq ft.

We’d round that down a bit further and call it 750 sq ft.  Or, alternatively, because you are using real dimensions rather than trying to give a generic example, now is a good time to start mixing and matching the actual dimensions of panels to the space on your roof.

For this exercise, we randomly chose a fairly standard size panel, measuring 39.13″ x 65.04″, which we’ll call 40″ x 66″ for our calculation.  These panels are rated at about 250 watts, which means that each ten square inches of panel is giving you almost 1 watt, or, if you prefer, each square foot is giving you about 13.5 watts.

Now let’s first do a ‘perfect world’ calculation.  Our roof has 52′ x 18.7′ dimensions, or 624″ x 224″, which is 139,776 square inches.  Our panels are 2640 sq inches each, so in theory, we can somehow fit up to 52.9 panels on the roof.  If we do the quick rule of thumb and reduce that by 20% (for aisle-ways), that points to 42.4 panels, which we’ll round down to 42.

That suggests our roof can provide a maximum of 250W x 42 panels, = 10.5 kW of power.  That’s actually a reasonably good number for most retreats and most purposes.  These panels would cost about $9,500, plus extra for mounting accessories, mounting, wiring, and so on.

If you were keen to maximize the power from your roof, you could get slightly more efficient panels that generate 275 watts from the same surface area.  But these more efficient panels are also very much more expensive – your cost for 42 panels is likely to increase from about $9,500 up to about $14,600, while your power output will go from 10.5kW up to 11.55 kW.  You’re paying an extra $5,100 for 1 kW of extra generating capacity – that’s a lot of extra money, and maybe it is better to think about spending the money to adapt your roof so it can accept four more of the standard panels (which would add the same additional capacity), or perhaps, use the money to build a shed and put the panels on top of that.  You need an extra 75 sq ft for the four extra panels.

Another approach is to have more of your roof pitching up in the southerly direction, and less or none in the northerly direction.  This will raise the maximum height of the structure, but if that’s not a problem, then go for it.  You’re sure to find a use for the extra internal space you are creating, too.

Personally we generally prefer to have more low efficiency panels rather than fewer high-efficiency panels.  Not only is it cheaper, but the loss of a single panel is not so serious, and our sense is that lower efficiency panels might be more reliable and ‘less stressed’ than higher efficiency panels.  But we have nothing to back up that perception.

If your target power generating capacity is around 10 kW, then you don’t need to do anything more at this stage.  You know that for 10 kW, you’ll need 40 panels, and you know that your roof has enough space for up to 52 panels, depending on layout and service lanes, so clearly that is going to work.

But if you are keen to get every possible watt you can, and you’re thinking of paying a great deal more for higher efficiency panels, now is the time to do an actual layout diagram for how your roof could be set out, using the cut out shapes.


We provided a couple of rules of thumb in this article.  There’s one more rule of thumb, or perhaps assumption, that seems fair.  It is probable that you’ll want to cover your entire roof with solar panels; especially if you have a multi-level retreat (ie more total floor area, and more living space, but with a smaller footprint and roof area).

The information in this article helps you understand how to calculate how many solar panels you can get on your roof.

May 052014
The Champion 3100W inverter/generator - currently our pick as best small inverter/generator for Level 1 type situations.

The Champion 3100W inverter/generator – currently our pick as best small inverter/generator for Level 1 type situations.

(You can see our definition of levels one, two and three type events here.  It is a useful categorization that provides structure to your problem analysis and preparation planning.)

When some people – particularly preppers – start thinking about generators, they immediately think of enormous noisy diesel standby generators, in special generator sheds, and capable of providing tens of kilowatts of power for extended periods, drawing off multi-hundred gallon storage tanks.  Don’t get us wrong.  We love diesel generators with a passion, and we also agree there’s no such thing as ‘too much’ power.

But these types of installations will typically cost $10,000 and up, will guzzle gas at a rate of several gallons an hour, are definitely impractical for apartment dwellers, and frankly are overkill for the times when you have a short power outage lasting anywhere from a few hours to a few days.  In these short time frames, we can compromise some of the convenience we normally enjoy with abundant and available power throughout our home, and also avoid needing to adjourn to our retreat to ride out the problem.

All we want is a small convenient and ‘low profile’ portable generator that we can run without drawing way too much attention to ourselves, and keep the essential parts of our home operating.

No matter if you have major industrial-grade generators or not, we suggest everyone should have one of these small generators – and here’s the key concept.  Get a small one.  Don’t ‘over-engineer’ the problem and end up buying something that generates enough power for you to have every appliance in your house all operating simultaneously.  For a short outage, all you need is lighting, some essential electronics, and some power to share between your fridge and freezer at times, maybe a stove top or other cooking facility at other times, and perhaps heating or cooling at still other times.

How Much Generating Power Do You Need?

We repeat.  Don’t over-engineer things.  And note the question.  We’re not asking how much power you want, or would like.  We’re asking how much you need, in order to sustain life and a moderate level of comfort and security, for a short duration of no more than a few days.

So, to sustain life, you need air, shelter, water and food, right?  Let’s think about each of those.

Air – hopefully you already have air!  And hopefully also you can get fresh air without needing to drive some sort of fan or other motorized appliance.  So presumably this does not need power.

Shelter – a bit more complicated.  We’re assuming that you’re in your regular residence and it is unharmed, so you have four walls and a roof already.  But also part of shelter is some amount of heating or cooling.  You know the seasonal weather extremes for where you live and you also know what you have installed in the form of hvac appliances.  But perhaps for a short-term solution, you should not aim to heat/cool your entire residence, but work out a heating/cooling plan for just a couple of rooms only.

Maybe you have a central hvac system, and in the winter you only need a small amount of power to drive the fan, with heat coming from natural gas.  That would be ideal, and natural gas seems to continue flowing, no matter what happens to the power.  But, even so, humor yourself next winter-time.  Do a ‘what if’ worst case scenario test and see how many 1500 W heaters you would need to keep a central living area warm without your hvac.  Hopefully you’ll be able to get by with only one.

As for summer, again perhaps you have a central air system, but for the purposes of this exercise, can you also have a window unit that controls temperatures in just one room?  A small generator is probably inadequate to handle the power needs of a central air system, but is probably suitable for a typical RV sized 13,500 – 15,000 BTU type unit.

One other part of shelter – some lighting.  Perhaps now is the time to start picking up LED lights when you see them on sale, so that you are getting maximum light for minimum watts.  Indeed, the LED lighting is so good (and so long-lived) that there’s no reason not to use them all the time, in all your lights.

So – heating, cooling, and lights.  That’s pretty much everything you need for short-term shelter requirements, right?  Maybe you have something else to also plan for, like a cellar sump pump?  Try not to overlook anything else that might be essential.

Water – do you have any water pumps (under your control, as opposed to operated by the building you live in)?  If not, then hopefully (maybe) you’ll continue to get water from your taps during a power outage, and if you don’t, that’s a matter for another article.  And what about waste water?  Some people have macerator units on their toilets, or pumps operating their septic system, but other than that, most of us have gravity powered waste water systems (at least out of our house, beyond that, in the city system, there might be other issues, which are again outside the purview of an article about low powered home generators!).

The only other consideration about water would be if you wanted warm/hot water.  If you have gas water heating, maybe you have an electronic pilot light (although these are not so common on hot water heaters) in which case you need power for the hot water to work.  Otherwise, if you have electric hot water heating, that will be a problem, because the elements in your water heater probably draw 5kW – 10kW of power, and that is more than you should reasonably expect from a small portable generator.

There are two workarounds for that.  The first is a small ‘under sink’ type water heater.  The other is to simply heat up or boil water on your stove top.  Worst case scenario, if you have to go without long hot baths/showers for a few days, that’s truly not the end of the world.

Food –  There are a couple of things to consider when it comes to food.  The first is food storage – ie, your fridge and freezer.  Ideally you want to keep these powered up, at least some of the time, so you don’t have all the food in your freezer spoil, and so you are able to maintain a cool temperature in your fridge too, besides which, depending on the nature of the power outage, you might need that food to live on.  Find out how much power your fridge (and freezer, if separate) use when they’re running; we’ll tell you what to do with those numbers in a minute or two.

The second part of food power needs is cooking your food.  There are several ways you can prepare food using relatively small amounts of power.  Your microwave is an efficient and effective way of preparing many food items.  A small toaster oven is another choice, and a stand-alone hotplate/element is a third choice.  You might also want an electric jug/kettle for boiling water for coffee and other purposes.  Indeed, why limit yourself – get all these items (if you don’t have them already).  None of them cost much more than $50 a piece at Costco or on Amazon.

Make a note of the power requirements for such items.

Everything Else – Okay, now we’ve covered the absolute essentials, but what else might also appear on a list of things you really need to be able to provide power to?  We’d certainly agree that you need to have half a dozen watts on hand for your phone charger, and maybe a few more watts for a radio or even a television.  For that matter, in the unlikely event that your internet connection is up, we’d not begrudge you the power cost of turning on your cable modem, Wi-Fi router and computer for an hour or two, a few times a day.

Maybe you have some medical equipment you need to operate.  And maybe you don’t want to have your generator running 24/7, and so have some batteries that you charge during the day and run your essential nighttime electrical circuits from at night.

Adding it All Up

Now that you’ve made a list of all the items you need power for, you’ll see there’s probably nothing on the list that needs to be receiving power, every hour, every day.  So this is where you now get to make a little bit of power go a long way.  You do this by letting your appliances take turns at the power from your generator.

For example, you know you’ll only need cooking appliances on a couple of times a day.  You also know that your fridge and freezer can go quite well for an hour or so (fridge) or half a day or longer (freezer) at a time with no power (especially if you keep their door shut!), and you also know that you can ‘play games’ with any heating or cooling, so that some of the day it is on, but some of the day it is not.

So what you should do is arrange it that you either have a cooking appliance, a fridge or freezer, or some hvac equipment running, but never all of these items at the same time.  How do you do that?  Simple.  Have plugs from all the devices sharing one (or two) sockets.  That way you can only have one item plugged in at a time.  Maybe you have some devices that would take up all the power, and three or four other devices that could run, any two at a time, and one or two devices that can be on or off at any time and it doesn’t really matter, because the power they draw is so low.

What you’d do is you’d have the output from your generator going first to a power strip that has all the small power devices connected to it, and one remaining socket.  You would have a collection of plugs next to this socket, and obviously only one of them can be plugged in at a time.  You might have a plug for your a/c, and another plug going to something else, and then one more plug that goes to a second power strip, on which you’ve blocked out all but two of the sockets, and you have a collection of plugs alongside that, so that any two of them can be connected at the same time.

That way it is physically impossible to overload your system, because the way you have your plugs and sockets lined up prevents that.

You can – and should – also have a power meter in series with all of this to monitor the actual power draw (see below).  Or perhaps manage all this with an Arduino based power management system.

Allowing for Surge and Starting Power

Most electric motors draw considerably more power when they are starting than when they are running at their normal speed.  This surge or starting power draw can be two or three times their running power – in other words, a 1 kW motor might have a surge/start power demand of 2.5 kW.  Some types of motors will draw as much as four, five or six times their normal running power while starting up.

This surge/starting power can last for as little as half a second or as long as three or four seconds, and starts off at the very highest level and then steadily declines down to normal running power at the end of the startup phase.

Most traditional generators will quote you two ratings – a rated or standard load, and a peak or maximum load.  So if your theoretical motor, with its 1 kW normal power draw and its starting power requirement of 2.5kW was to be matched to a generator, you should get one with a rated or standard load of at least 1 kW and a peak or maximum load of at least 2.5 kW.

But what say you have four devices, each of a 1 kW standard load and a 2.5 kW starting load?  Does that mean you need a 4 kW generator that can handle a 10 kW peak?  Happily, no.  It is normal to assume that you’ll never have multiple devices all starting simultaneously.  Because the starting load is so brief, and also quickly starts dropping down from maximum, this assumption is usually acceptable in most environments.  So in this example, you’d want a 4 kW generator with a 5.5 kW max load rating.

Choosing a Suitable Small Generator

Our expectation is that you’ll end up with a power need in the order of about 3kW; maybe a bit less, and if it is much more than that, you’ve failed to correctly differentiate between ‘need’ and ‘would like’!

The good news is that there are very many different models in this general power range to choose from.  But that’s also the bad news.  How to make a sensible buying decision with so many choices?

Well, there are a few things to consider that will help steer you in the right direction.

The first is that you want the generator motor to be four-stroke not two-stroke (ie separate oil and gas, rather than mixing the two together).  Four stroke motors tend to be more fuel-efficient and more reliable.

The second is that you want the generator to be as quiet as possible.  Some generators publish ratings on how noisy they are, but unfortunately there’s no universal standard for how this should be measured.  If you see a noise rating, it should be quoted in either dB, dBA, dBC, or possibly some other type of dB measurement.  It would be helpful to know if it was measured at full load, half load, or idle (there can be more than a 10 dB difference between idle and full load), and at what distance from the generator the measurement was made.  Was it in an open area or an enclosed room?  Was it a hard concrete floor or something more sound absorbing?

It is difficult to convert between the different type of decibel measurements, because the different weightings or adjustments that are implied by the letter A, B, C or D after the dB vary depending on the frequency of the sound being measured.  As a rule of thumb, though, the same sound probably registers lowest on the dBA scale, and slightly low on the dBC scale, and higher on the plain dB scale.  You’ll seldom/never see dBB or dBD.  Oh, to add to the confusion, some suppliers sometimes use the term dB and dBA interchangeably, even though they are actually very different.

You can sometimes get a sense for how loud generators are, even if they are not specified, by reading reviews on sites like Amazon.  Chances are someone will compare any given generator’s sound level to another generator, and then you can start to work from there to understand at least the relative loudnesses, and if one of the generators does have a published sound rating, then you know if the other one is above or below that figure.

A good generator has a sound level of under 60 dBA under at least half load when measured on a concrete floor from 7 meters (23 feet) away and with reflective walls 100 ft (30.4 meters) away, and with a very quiet ambient noise background (ie 45 dB).

Another relevant issue is fuel economy and run time.  These are two slightly different measures.  Fuel economy can be thought of in terms of ‘how many kWh of energy will this generator give me per gallon of gas it burns’.  An easy way to work that out is to see how many gallons of fuel an hour it burns, and at what load level.  For example, a 4 kW generator, running at 50% load, and burning 0.4 gallons of fuel an hour is giving you (4 * 50%) 2 kWh of energy for each 0.4 gallon of fuel, ie, 5 kWh per gallon of fuel.  The more kWh per gallon, the better.

The run time issue is similar but different.  It simply measures how long the generator will run on a single tank of gas.  Sure, the more fuel-efficient the engine, the longer each gallon of gas will last, but probably the biggest factor in run time is simply the size of the gas tank on the generator.  Run time means nothing when trying to get a feeling for gallons/hour of fuel use, unless you know how many gallons in the tank that are being consumed.

In theory, you should turn the generator off when re-fueling, and even if you don’t do this, it is always an inconvenient hassle, and so the longer the run time per tank of fuel, the happier you’ll be.

Make sure you understand, when looking at a run time claim, what the load factor on the generator is.  Needless to say, all generators will run much longer at 25% load than at 100% load.

One other nice feature, although one to be used with caution, is a 12V DC power outlet that might be suitable for some crude battery charging, depending on what its true output voltage might be.  But be careful – charging batteries is a very tricky business and perhaps it is more sensible to charge the batteries through a charge controlling device, and from the generator’s 110V main output.

An obvious consideration, but we mention it, just in case, is the generator’s size and weight.  The smaller it is, the easier it is to store somewhere convenient, and the lighter it is, the easier it will be to deploy when you need it.  Oh – do we need to state the obvious?  Don’t run a generator inside.  You must keep the motor exhaust well away from the air you breathe.

Something that is often underlooked or obscured is the quality of the a/c power and its waveform.  How close to a pure sine wave is the power that comes out of the generator?  This doesn’t really matter for resistive loads like a heater, but for motors and electronic circuitry, the ‘cleaner’ the wave form the better.  The only way to be certain about this is to connect the generator output up to an oscilloscope, but that’s not something that is easy for many of us to do.

There is a new type of generator now becoming more prevalent which not only has an excellent pure sine wave form of a/c power, but offers a number of other benefits too.


(Note – do not confuse an inverter/generator with a standalone inverter.  A standalone inverter converts DC power to AC power, typically from 12V DC up to 110V AC.  It does not have a generator connected to it.)

A typical generator (well, what we call a generator actually is a motor that runs an alternator) runs at a steady speed of 3600 rpm so that the power that comes out of the alternator will be automatically at 60 Hz (mains frequency).  The a/c waveform will be a little bit rough and noisy, which can be a problem when powering more delicate electronics.  Also, the engine is having to run at 3600 rpm, no matter if it is heavily loaded or very lightly loaded with power consuming devices because the frequency of the power generated is dependent on the speed of the motor.  This makes the motor noisier than it needs to be, and at lower power loads, makes it less efficient because it is using a lot of power just to spin itself around.  If the engine speed should fluctuate, so too will the frequency of the supplied power and that also can cause problems with electronic items.

Modern high quality generators take a different approach.  They generate a/c power at any frequency at all – it doesn’t matter what frequency, because they then convert the a/c power into DC power.  Then, in a second stage, they use an electronic inverter to convert the DC power into (at least in theory) a very clean pure a/c sinusoidal wave form at 110V.  You have a much nicer wave form, and because the generator can spin at any speed, the generator does not need to be so powered up if generating only a light load of power, making it typically quieter and more fuel-efficient (up to almost 50% more fuel-efficient).  On the downside, inverter/generators are currently more expensive, and have slightly more complicated electronics.  But for the type of application we are considering, they are usually vastly preferable.

Some inverter generators have a nifty feature.  You can double them up – if you connect the generator to another identical generator, using a special connecting cable that synchronizes the a/c output waveform of the two generators together, you can get twice the power.  You might say that it is better to have two 2kW generators rather than one 4kW generator, because that way, you have redundancy.  Anything could fail and you still have half your generating power.

Another nice thing about most inverter/generators is that they have been designed, right from the get-go, to be small, compact, lightweight, and quiet.  That’s not to say that they will be totally undetectable when operating, but they won’t be anything like as noisy as traditional generators that can be as loud as motor mowers, and if quiet operation is really important to you, some additional external baffling in the form of some sort of operating enclosure could drop the sound level down even further.

Their compact size and generally light weight makes it practical for them to do double duty not just as an emergency generator that gets ceremonially wheeled out of the garage when the power goes off (or, even worse, that resides in its own special building), but also as a go anywhere/take anywhere general purpose generator, useful for outdoors events, camping, remote building sites, and so on.

An obvious consideration for any generator is the cost.  With the constantly changing mix of models, ratings, and prices, we’ll not get too specific other than to observe that at the time of writing, it seems you’re likely going to be writing out a check for a little less than $1000 for a good inverter/generator with about a 3 kW rating, which is about twice what you’d pay for a regular generator without the inverter stage.  We expect this price differential to drop, but please don’t wait for that to happen before you get one!

Here is Amazon’s current listingof gasoline fueled generators.  Some are inverter/generators, others aren’t.  Some are California emissions compliant (CARB), others aren’t.

If we had to select a favorite, we’d probably nominate the Champion 3100W unit, or failing that, one or a doubled up pair of the Champion 2000W units.

How to Measure the Real Current/Power Used by Your Appliances

Devices such as this, costing $16 - $26, show you exactly how much power every one of your appliances consumes.

Devices such as this, costing $16 – $26, show you exactly how much power every one of your appliances consumes.

Maybe you have a computer with a 450 watt power supply.  Does that mean the computer actually is drawing 450 watts of power all the time it is on?  Almost certainly, not (a typical computer might consume only 50W of power, maybe even less, plus another 50W of power separately for its screen).  Maybe you have something else with a power rating plate on the back ‘110V 10A’ – does that mean it is drawing 10 amps all the time it is on?  Again, probably not.  A 10A rated device probably includes all lesser amounts of power too, and they simply put 10A on the plate as a conservative overstatement that wouldn’t cause them problems in the future.  (Note – resistive devices such as heaters tend to have more accurately plated power requirements.)

It is normal for appliances to show their theoretical maximum power draw rather than their normal power draw on their labeling.  While you need to leave a bit of ‘headroom’ to allow for occasionally one or another of your appliances peaking up higher to full power, it is acceptable to assume that most of the time, most of them will be using average rather than maximum power.

So how do you work out how much power your appliances are really truly drawing?  Easy.  There are devices that you plug in between the appliance and the wall, and they measure the power consumption of whatever is plugged into them.  Indeed, you don’t need to plug only one appliance into one of these measuring devices – we’ll sometimes plug a power strip into the measuring device, and then connect a bunch of equipment to it.

As you can see, Amazon sell such units for as little as $16.  Although there are some new low price units, we have always bought the only slightly more expensive Kill a Watt brand monitors.  You only need to get one to be able to work your way around your house testing everything.

In addition to showing you the instantaneous power usage, the Kill a Watt unit has another useful function – it can also show you total energy used over time.  When would this be useful?  Think of something that cycles on and off, such as your fridge.  You can measure how much power it uses when it is on, and you can guesstimate how much extra power to allow for when it first starts up, but how much power does it use per day?  Unless you stand over your fridge nonstop, day and night, carefully noting the minutes it is on and the minutes it is off, you’ll have no accurate way of knowing this.  But with the Kill a Watt meter, you simply plug the fridge in, check it is zeroed, then come back in a day or two and note the total hours elapsed and the total kWh used.  How easy is that!

(Note that if you are doing these calculations, you should check for different total energy consumption rates based on hot and cold weather, on opening the fridge a lot or a little, on placing hot foodstuffs into the fridge, and so on.  You’ll find that your daily average usage will vary enormously from some ‘good’ days to some not so good days.

How to Measure the Actual Power Being Provided by Your Generator

Your objective, much of the time, will be to run your generator at about 75% of full power.  At power levels much above this, or at power levels much below 50%, your economy will start to suffer and you’ll be getting fewer kWh of electricity per gallon of gas.

But how do you know how much power you are taking from the generator?  Easy.  Use the same Kill a Watt meter you used to calculate your power draws, and plug it into the generator then plug all power loads into a power strip plugged into the Kill a Watt.  That will tell you exactly the power you use.

You can use this information to know when you can add extra power loads to your generator, and when you are close to maxed out.

Two Notes About Fuel Storage

Many cities and many landlords have restrictions on how much fuel you can store at your residence, and probably also on the types of containers you can store the fuel in.  Sometimes these limits are per address, sometimes they are per building (which might mean you could keep fuel in a garden shed as well as in your garage and as well as in your house, too).

Enforcement of such bylaws is typically done ‘after the fact’ – ie, if you have a fire and it becomes apparent you had a mega-fuel dump in your garage, then you may find yourself being asked some awkward questions, not only by the fire marshal, but quite likely by your insurance company, too.  By the way, it is not always easy to tell, after a fire, exactly how much fuel was stored in each container, particularly if they were all in the one area.  It is probably possible to see how many fuel cans you had, but harder to tell which ones were full, which were half full, and which had only a couple of pints in the bottom.

It might pay to familiarize yourself with these requirements, and if you have a large number of half empty fuel containers, you better be sure you can explain why.

That also points to another benefit of a fuel-efficient low powered inverter/generator.  If you are trying not to trespass too far into ‘forbidden territory’ in terms of the fuel you store, then the more hours you can run your generator on a small amount of fuel, the better.

Secondly, gasoline (and most other liquid fuels) has a surprisingly limited life.  You can store it for three months with no ill effects, but after about six months, you’ll start to encounter problems.  Our article about fuel storage tells you more about these issues and also recommends the best form of fuel life extending chemicals.

Maintaining Your Generator

We hate internal combustion powered equipment, and avoid it wherever we can, particularly for things we only use rarely.  They can be difficult to store and unreliable in operation after extended storage.  Electrically powered items are generally very much better.

But in the case of a generator, you have no effective alternative to some sort of internal combustion powered device, and so you’ll need to be attentive to the manufacturer’s recommendations about periodic maintenance.  Not quite so clearly stated is the need to also be sensitive to the age of your fuel and managing that, so you aren’t running old untreated fuel in your generator.  Also not stated, but in our opinion very important, is to run your generator for several hours, perhaps once a quarter.  Solstices and equinoxes are the trigger dates we use for all sorts of maintenance items (other people use daylight saving start/end dates for things that need maintaining less frequently).

One other thought.  It might be useful to keep a spray can of engine starter fluid as a way of helping your generator come to life if it has been too long since it last ran and it is proving reluctant to start, particularly on a cold day.  Some generators start more readily than others.


A small, lightweight, and almost silent emergency generator can allow you to keep power on in your normal home, even when the lights are out all around you.  While we have nothing against larger systems that will power your entire home (and have one ourselves), if you’re not ready for a ‘full-on’ system and the costs and complications associated with it, a simple portable inverter/generator will give you enough power to make the difference between great discomfort and only moderate inconvenience.

These small units are also invaluable for apartment dwellers.

May 042014
This Avometer advertisement appeared in 1953, and offers the meter for £23.50, twice the average weekly wage at the time.  Similar meters today can cost only $23, closer to the average hourly rate.

This Avometer advertisement appeared in 1953, and offers the meter for £23.50, twice the average weekly wage at the time. Similar meters today can cost only $23, closer to the average hourly rate.

As we imagine and plan for a difficult life in the future, we realize that we will need to learn more skills than we currently have, because when things go wrong, we can’t simply go out and buy a replacement, and might not be able to find anyone conveniently nearby to fix the problem, either.

Hopefully you’ll continue to have at least some electricity at your retreat, and will be able to enjoy the extraordinary benefits that electricity has given to us all.  If you want to get a taste for just how extraordinary, beneficial, and essential those benefits are, treat yourself to a weekend with no electricity.  Turn off the main breaker in your fuse box on Friday night, and don’t cheat by using any batteries.  Go totally electricity-less for a weekend, and do it not when the weather is comfortable outside, but when it is either impossibly hot or impossibly cold.

Okay, now that you’re back reading the article again, and fully convinced about the essential role electricity has in your life (how long did you last before turning the breaker back on?) there’s every chance that at some future point, you’re going to have to become an amateur electrician, and maybe even an amateur electronics repair tech too.

You’ll not be able to repair anything if you can’t first troubleshoot to find out the problem.  Ideally, you’ll also want to be able to test the repair before making the fixed device ‘live’ once more, too.  Now the good news, particularly with electrical (as opposed to electronic) devices, is that many problems can be troubleshooted using that most sophisticated of instruments, the Mark I Human Eyeball.  You’ll spot breaks in cords, blown fuses, burned out plugs, and so on, just by looking.

But whether it is for troubleshooting, or for checking the correctness of repairs before plugging the devices back into your main power circuits, you’ll find everything you do will be immeasurably assisted by what is termed a ‘multi-meter’ – a device that will show you various things about electrical circuits – in particular, both amps and volts for AC and DC circuits, and also ohms for resistance, and with multiple scales ranging from fractions of a volt/amp/ohm up to tens of amps, probably thousands of volts and millions of ohms.

The first ever multimeters came out in 1923, and were the result of a British Post Office technician getting exasperated at having to carry so many individual test meters with him (and back then they were all big, bulky, and heavy, too).  His creation was the Avometer (Avo being an acronym for Amps, Volts, Ohms), and when first released it had seven different functions (three DC voltage ranges, three DC amperage ranges, and one resistance range).  When the Avometer finally and sadly ended production in 2008, it had 28 ranges, also now including AC volts and amps.

In the past, Avometers often cost more than a couple of weeks wages for the technicians using them, so they were hardly a commonplace device that people would have ‘just in case’ they might need it in the future.  But in time, more manufacturers started making similar devices, and with less robust but more automated manufacturing methods and standards, and so prices dropped amazingly.  I remember buying one as a teenager, very many decades ago, and at the time never gave thought to how such devices once cost hundreds of times more than they did then – and today, they are even cheaper still.  You can buy a reasonably multimeter from somewhere like Harbor Freight, or on Amazon or eBay, for under $20, and an excellent one for under $40.  So there’s no reason why you shouldn’t have one.

What To Look For When Choosing a Multimeter

A typical multimeter will be able to test at least five different things – DC and AC volts, DC and AC current, and resistances.  There are differences between meters, however, in terms of the minimum and maximum values it can read for all five of these scales.

Needless to say, you’d like a meter that has the broadest range of scales, but in terms of what you really need, if you are using your meter mainly for testing electrical devices, you probably need to be able to read DC volts from a minimum of maybe one or two volts (ie perhaps a 10V scale) up to a maximum of less than 1000V; DC amps from perhaps a 1A or 0.1A (100 milliamp) scale up to maybe 10A; AC volts from perhaps a 10V up to a 1000V scale; AC amps from perhaps a 1A scale and up as high as possible; and resistances from as sensitive a scale as possible (maybe a max of 10 kOhm on the scale, and showing individual ohms at the low-end of the logarithmic scale) up to showing maybe a 10 MOhm maximum scale).

If you will be using your meter for electronic troubleshooting as well as electrical troubleshooting, you might want to have some additional scales to show lower values for DC volts and DC amps, and probably a lower AC amp scale too.  You might also want to be able to read higher current flows too – this will likely require a specialized device (see below).

If you need other ranges beyond these, you’ll probably know about your special needs already.

A nice feature is a continuity buzzer.  This is useful when you’re doing mundane tasks like checking to see which ends of which wires relate to the other end of the same wires, or checking for breaks in circuits.  Instead of having to watch your meter, you simply touch your probes to things and if there’s a clear connection between the two things you are touching, the meter will buzz or beep.

It helps to understand, for the AC measurements in any meter, what range of frequencies the AC measurements are accurate for, and what types of waveforms it will accurately read.  If you’re just reading mains power type frequencies, then most meters will work well for that, but if you have unusual wave shapes or are wanting to measure audio or radio frequencies as well as mains frequency, then you will need a specialized meter that measures true RMS and higher frequencies.

Some meters have additional functions, including the ability to measure frequency, capacitance, inductance, temperature, diodes and some functions of transistors.  You’ll of course pay extra for such extra features, but if they have value to you, then why not get the ability, particularly because these extra functions don’t necessarily add much more to the price of the meter.

See further discussion in the section on analog or digital meters, particularly for some features that are unique to digital meters.

A meter should have at least one fuse in it to protect its circuitry from overload.  This is particularly essential in analog meters, where the meter’s integrity relies on you, the user, selecting the correct scale to start with whenever you connect the meter to anything.  Old hands know the rule ‘always start with the highest value range setting, and then switch down as needed’ from bitter experience.

Our point here is to identify the type of fuse used and to lay in a small supply of spares.  In the worst case scenario, if you blow the fuse, you can replace the fuse with regular wire or any other sort of fuse as well – the meter will continue to work, but it will no longer be protected, so your next mistake will probably fry it.  We’ve only once ever blown a fuse, so you probably don’t need to have too huge a supply of spares.

Accuracy Issues

Different meters make different claims about their accuracy, and some digital meters display more digits than others – indeed, they’ll probably display a more detailed number than their underlying accuracy allows.  By this we mean a meter that has an accuracy of +/- 3% might have a three or more digit display, so it could in theory show, say, 97.2 volts, whereas the actual voltage could be anywhere from 94.3V up to 100.1V – so what is the sense in telling you about the 0.2V when even the 7 volt part of the reading can vary widely from 4 up to 10.

Don’t get too hung up on accuracy issues.  Most of the time, the required value and tolerance of anything in typical electrical (and electronic) circuits is fine if it is within about +/- 5% of the optimum value, and sometimes you’ll find that +/- 10% is still perfectly acceptable.

Better analog meters will have a mirror on their scale.  This enables you to directly line up the angle between yourself, the needle, and the scale and avoid any parallax errors when reading values from the scale.  The bigger the scale on an analog meter, the more accurate the readings you can get from it.

A possible exception to our suggestion you don’t need a lot of accuracy would be reading the voltage of your input power supply.  Noting that power varies according to the square of the input voltage, if your voltage varies by only 10% from specification, the power available to your device will vary about 20%.  That can lead to not-obvious problems that end up burning out motors and frying electronics, so you probably want a meter that has reasonably good accuracy on whatever scale you’ll use to measure input voltages into devices.

One type of accuracy is important.  Whenever you connect a meter to a circuit, you actually change the nature of the circuit, and so the reading you get from the meter will be influenced by the fact that the meter has been connected to the circuit.  This is not really a worry when working on mains level voltages and multi-amp currents, but it can become significant when working on very low voltage and very low current electronics.  Most digital meters are very much better than most analog meters in this respect; if you are getting an analog meter, make sure it is rated at 20 kOhms/volt or higher (a measure of the impact of the meter on the circuit it is testing).  Digital meters should have an impedance of at least 1 Megaohm, and 10 MΩ would be better.

Analog or Digital Multimeters?

A great value analog meter, the Mastech YX360.

A great value analog meter, the Mastech YX360.

The big question you need to answer is whether you should get an analog or digital meter.  Analog meters have an ‘old fashioned’ dial and needle that moves across it, and digital meters of course have a digital digit display.

For an uncertain future, you should use as low-tech a product as possible.  An analog meter would be the best way to go in such a case, because it has almost no electronics at risk of being ‘fried’ by an EMP, and it does not require any power to read volts and amps (but it will unavoidably need a battery to be able to read resistances, due to the way that resistances are tested).  On the other hand, digital meters are very much nicer and more convenient and flexible, all of which is dangerously tempting!

Talking about batteries, make sure your meter uses a typical/common battery and voltage.  Don’t be tempted to go out and buy a lovely old antique Avometer, for example.  Although we have one ourselves, it is more as a museum/display piece than an everyday part of our test gear, because it uses a unique type of 15V battery that is, for all practical purposes, no longer available.

The higher the meter’s battery voltage, by the way, the better it will be able to measure high values of resistance.

A great value fully functioned digital meter, the Mastech MS8268.

A great value fully functioned digital meter, the Mastech MS8268.

Digital meters of course need power (usually from their battery) for everything they do, but their power needs are very low, and we find that the batteries in our digital meters last years at a time.

Interestingly, whereas analog meters are possibly more electrically and electronically robust, digital meters are more physically robust.  If you drop your analog meter, you might destroy it (the indicator needle is on a very sensitive bearing), but if you drop your digital meter, you are much less likely to harm it.

Digital meters have a lot going for them.  Better ones have auto-ranging, so you don’t have to worry about frying the meter by setting it too sensitively for whatever you are measuring.  They are generally a bit more accurate than analog meters too, but see our comments about accuracy above.  On the other hand, some people like to be able to see the swing of a needle which can sometimes help you better understand exactly what you’re seeing when troubleshooting, and of course this is only possible with an analog meter.

Digital meters usually have auto-polarity, so there’s no need to hassle over connecting the positive lead to the positive side of a circuit, and the negative lead to the negative side.  Better analog meters will have a polarity switch so you can simply slide the switch rather than reverse the leads if you get it wrong.

Some digital meters will have added functions such as ‘hold’ which locks in the display the value when you pressed the hold key.  That way if you forget it, you don’t need to remeasure because it is still on the display.  Sometimes you might also see the ability to capture minimum and maximum values, too.  This can be helpful, particularly if you are not staring nonstop at the meter, and have a problem you think might be due to occasional spikes or drops in power.

An auto-off feature is really nice – it saves you if you forget to turn the meter off; you don’t have to worry about running your battery dead.

If you are getting a digital meter, make sure it has a light switch on it so you can turn on a backlight and read the LCD display if you are somewhere with low ambient light.

So, yes, there are lots of benefits to getting a digital meter.  Our suggestion, noting how inexpensive both digital and analog meters are these days, would be to get one of each.  That also allows for the adage that a well prepared prepper has at least two of everything essential and important.

Which One to Buy?

Here’s a listing of analog multimeters from Amazon.  We’d probably choose the Mastech YX360 as a great value analog meter.  It seems to also be sold under different names by other companies, too, but generally at a slightly higher price.

Here’s a listing of digital multimeters, also from Amazon (of course).  You’ll see some units for under $10, but we’d probably splurge and spend not quite $30 to get this truly impressive Mastech MS8268 meter.  Indeed, although we have a shelf full of meters already, we liked this meter so much that we went out and bought one while writing this article!

High Current Ammeters and Clamp Meters

The Mastech $45 AC and DC clamp meter.

The Mastech $45 AC and DC clamp meter.

A problem that is common to most analog multimeters is that they have difficult reading high amp values, because they are built around a meter that is very sensitive, rather than one which is very insensitive, to current flows.

An inconvenience that is also common to all regular meters, is that to read the current flow – the amps – in a circuit, you need to cut the circuit open and connect the ammeter in series with the circuit.  When testing volts, you simply place the voltmeter in parallel across the circuit, which is usually a much easier thing to do.  (Oh yes, as for testing resistances, that can be the biggest hassle of all, because you have to isolate the thing you are testing from everything else before you can get an accurate reading.)

There are of course solutions to these issues.  You can get dedicated high-current reading ammeters and connect those in series in such circuits.  Or, in the case of AC current in particular, you can get a ‘clampmeter’ which is a device that you simply place around one of the wires.  The clampmeter senses the magnetic field created by the flowing AC current in the wire, and so displays the measured current in the wire without you needing to penetrate/cut the wire at all.

Due to the way they work, they are not so good at measuring small amounts of current (ie under one amp) but they are excellent for measuring large currents, potentially up to several hundred amps.  They are also inexpensive, and of the ones listed on Amazon at present, we think this one is probably the best buy (ie just under $30, and with scales all the way up to 600A) for most people and purposes at present.  There are other meters costing very much more, but offering not much extra in the way of useful features for most of us.

There is one feature which some of the more expensive clamp meters offer.  That is the ability to read DC current as well as AC current through the clamp.  If you might find this worth paying only a little extra for, something like this Mastech meter is probably a good choice, and still costing less than $45.

These are wonderful devices, but note they only work when placed around one of the wires in what is usually a two and sometimes three or four wire circuit.  If you place it around both wires in a typical AC power lead, the magnetic field from one of the wires is essentially cancelled out by the field from the other wire, so you will need to somehow separate the wiring to put the clampmeter around one of them.  You might find a very short extension cord where you’ve opened up the wiring between the male and female ends, allowing you to then clamp around whichever wire you wish, will be helpful in such cases.  (In theory, of course, you’ll get the same current reading from either the phase or the neutral wire, and hopefully you’ll get absolutely no current reading at all from the ground wire.)

There is another approach to this – there are wonderful line splitter devices such as this one on Amazon that not only split the line for you, but also have an extra section of line where the current signal is amplified ten-fold, enabling your clamp meter to pick up and display lower currents (for example, a 0.1 amp current would then read as 1.0 amps on the clamp meter).  At a cost of less than $15, this is a very useful thing when testing AC power around your retreat.


We suggest all preppers should have at least one multimeter as part of their tech/troubleshooting supplies.  If you are buying only one meter, and primarily for electrical purposes, perhaps buying a simple analog meter will not only save you money but also give you the most ‘future proof’ device.  But if you want vastly more capabilities, then you’ll probably choose to treat yourself to a digital meter as well.  And don’t forget a clamp meter too.

May 022014
A diagram showing how a fuel cell works.

A diagram showing how a fuel cell works.

This is a further part of our series on solar energy.  Please also visit our sections on energy in general and solar energy in particular for more related articles.

Chances are you’ve not even thought about hydrogen powered fuel cells as part of your retreat energy strategies.  For most purposes, fuel cells would indeed not be a good choice, but there’s one special scenario where they might be of relevance – as part of a way to store energy.

But, before you rush off to your local fuel cell store to buy a dozen (as if such a place exists!), you might want to read through this article and in particular, appreciate that whatever the advantages of fuel cells may be, there’s one also a disadvantage.  The technology for a ’roundtrip’ transfer of energy from electricity to hydrogen and back to electricity is expensive and not very efficient (on the other hand, it is not necessary any worse than other alternatives open to you).

You could be excused for stopping reading at this point, and we write the rest of this article mainly to provide a reference point you can track from.  We are sure that the technologies involved will improve over time, and you can match new products with the information here to see how much closer to practical affordability things are progressing.  Of course, if you do come across a relevant new improvement, please let us know so we can update the information here.

We’ll explain a bit about fuel cells in this article, and look at the plus and minus issues associated with storing your surplus energy (should you be so fortunate as to have any, of course!) in hydrogen and then converting it back to electricity via fuel cells.

What Fuel Cells and Hydrogen Energy Storage Involves

A fuel cell can be thought of as using the opposite process to that which causes the electrolysis of water.  When you electrolyze water, you use electrical energy to separate the water into its component hydrogen and oxygen.  When you use a fuel cell, you combine hydrogen and oxygen to create water and you get electrical energy produced as part of the process.  Other materials can also be combined, but hydrogen and oxygen is the most common, particularly because this means you only need to store the hydrogen, obtaining the oxygen from the air all around us.

Note that you could also run an internal combustion engine on hydrogen fuel, but this is nothing like a fuel cell.  A fuel cell has no moving parts and generates little heat and almost no noise, an internal combustion engine takes chemical potential energy, converts it to heat, and then converts the heat to motion, and then converts the motion to electricity.

Ecologists like fuel cells because the byproduct of running a fuel cell is simply water.  No noxious/toxic nitrogen or sulfur products, and no carbon releases.  What’s not to like about that (or so the ecologists ask/tell themselves).  But, as with most things, there’s a lot more to fuel cell technology than simply ‘burning’ hydrogen and oxygen and getting water and electricity as a result.

Fuel cell technology is both old and new.  It has been around in experimental form for a long time – the first were invented in 1838.  More recently, fuel cells have been used to generate power on the space station, and in experimental fuel-cell or sometimes termed ‘hydrogen powered” vehicles.  Fuel cells, in miniature form, are even used in portable electronics.

Not all fuel cells use hydrogen.  There are other chemical processes that can also be used (if the fuel cell is designed for it of course), but we are focusing on hydrogen fuel cells here because on balance, the ’roundtrip’ to generate hydrogen, store it, then use it in a fuel cell is probably the easiest and best for prepper purposes.

Although based on old technologies, fuel cells are also more in an experimental than a commercial state of being at present.  This is because there are issues with cost and efficiency that currently make them impractical for any type of regular normal use, but while the efficiency levels are very low, the promise of boosting efficiency holds out an exciting hope that fuel cells may become more commercially viable in the future.

Furthermore, if money is not a constraint, then the ability to store hydrogen for extended times with little loss is a huge plus.  Most other energy storage systems are not as practical as hydrogen if you want to store the energy not just for a day or two but for many months.

Hydrogen Related Issues

Even if fuel cells themselves become more efficient, there’s another step in the process that needs a lot of additional optimization – collecting/creating hydrogen and then distributing it to refueling points.

It is important to realize that while hydrogen is the most abundant element on the planet, and oxygen is all around us, that does not mean the cost to power a fuel cell is negligible.  Most of the hydrogen out there is currently ‘locked up’ in water (which is, as you doubtless already know, H2O) and extracting the hydrogen from water (or from natural gas – another rich source – CH4) – is expensive, as can also be the technologies to store and transport hydrogen.

On the other hand, as long as you have hydrogen stored in a leakproof container (slightly harder than it sounds!), it will keep forever.  This is the same as propane, but quite unlike petrol or diesel (see our discussion about storing liquid fuels), and also quite unlike other energy storage methods such as batteries or accumulated reservoirs of water for hydro power.  This is clearly a good thing.

The relevance of hydrogen storage and fuel cells for us preppers is as another way of storing energy.  If you are preparing for only a level 1 or low-grade level 2 event, maybe you’ll cover your energy needs by simply buying a generator and laying in an adequate supply of fuel for it, and possibly stick a couple of solar panels on your roof as well.  That’s a fine way to proceed, and it allows you to reasonably closely match your power needs as they vary during each day and night with the supply of power from the generator.  In such cases, however, you’ll not really ever find yourself in a situation with ‘too much’ power and wanting to find some good use for it.

But most of us, no matter what outcomes we are preparing for, will choose to use primarily renewable energy sources (ie wind and solar) for much/most/all our energy needs.  The huge problem with these energy sources is that their output varies widely, with the weather, and in an unpredictable manner.  As we discuss in articles such as ‘How Much Solar Power Generating Capacity Do You Need‘ and ‘How Much Extra Emergency/Reserve Capacity Does Your Solar Power System Need‘, it is necessary to develop more powerful than necessary generating systems so that they will provide close to sufficient power, even with very little sunlight (or wind).

The happy flipside of this is when the wind is blowing in its sweetspot speed zone, and the sun is shining brightly onto your solar panels in a cloudless sky.  All of a sudden, your power generation is providing you with two, five, maybe even ten or twenty times the power and energy you need.

There’s no such thing as ‘too much power’ of course, and there’s no problem or harm to your system if you simply choose to ignore the extra power that is coming from your generating system and ‘waste’ it.  But maybe you might also look at the downside of sometimes being very short of energy, and seek a way to capture and save/store some of this spare energy to then use when your system is struggling to provide the energy you need.  There are a number of ways you can do this, and the simplest is to go out and buy some more storage batteries.  But maybe you feel the need to shun simple, and prefer to seek out complex solutions!  Or, more seriously, maybe you want to spread your risk by having multiple technologies for every part of your retreat and its mission critical systems, and in such a case, a second method of power storage in addition to batteries might be worthy of some more investigation.

It would be possible to use this extra power to store hydrogen, and then when you need to use the stored energy, run the hydrogen through a fuel cell to regain the electricity.  That’s the simple theory of it, anyway.  Let’s look a bit more now at how it would actually work, and what problems you could run into.

Let’s think about this in three steps.  The first is how to ‘get’ hydrogen.  The second is how to store it.  And the third is using the fuel cell(s) to convert it back to electricity.

1.  Getting Hydrogen

There are two possible and somewhat practical ways of getting hydrogen.  The first involves the electrolysis of water, the second involves steam reforming of natural gas (ie methane); this latter method works well for large plants, but not so well for smaller domestic production.

So, if you look at electrolysis, while you could build your own electrolysis plant, perhaps you’ll simply choose a turnkey unit.  Ebay sells hydrogen generators, and we saw a listing for one that requires a maximum of 400W of power to generate up to 5L of hydrogen a minute.  In other words, if we believe its specifications, 1kWh of power would generate 750L of hydrogen.  Ebay has this unit listed for $12,000, and it is being sold by a Chinese supplier.

But, be warned.  Anything that talks about ‘up to’ has immediately given itself an enormous ‘loophole’ to invalidate its claim.  Up to 5L a minute includes all numbers less than that, doesn’t it.  We just do not believe, for an instant, this unit will consistently create 5L of hydrogen while consuming electricity at a rate of only 400W – if it was to do this, it would be unbelievably efficient, and several times more efficient than leading branded products with more credible specifications.  You’ll doubtless be shocked and horrified to learn that you need to tread cautiously when trusting the word of Chinese suppliers selling products through eBay!

Before we move on, let’s just point out one other thing about this unit.  It only draws up to 400W of power.  You are likely to have several kW of spare power capacity at good times that you want to divert and store.  So you might conceivably spend $36,000 for three of the units, and that still only gives you a way to divert 1.2 kW of power.  If you wanted to be able to divert 5 kW, then you’re looking at $144,000 for enough of these units, and clearly that’s no longer a sensible approach.

Let’s now look at another product with more believable specifications.  A Hydrogenics HyLyzer unit.  These will product either 1 or 2 Nm3/hr of hydrogen – that’s basically a fancy way of saying 1000 or 2000 liters.

The key part of the specifications given here is the disclosure that the unit consumes electricity at a rate of 6.7 kWh per 1000 liters of hydrogen created.  So a single unit would soak up your spare power at a rate of 6.7 kW.  To put that another way, each kWh of electricity creates about 150 liters of hydrogen.  Units can usually be run at maximum production rate (to use up the maximum spare power) or at lower rates (if you have less spare power).

Heavier duty larger capacity units (of a size probably impractical for us to consider) can be somewhat more efficient, perhaps requiring only 5 kWh per 1000 liters of hydrogen.

We understand but have not been able to get confirmation from Hydrogenics that these units cost in the order of $40,000.  Here are some apparently not quite so good units and their prices.

2.  Storing Hydrogen

The good news is that hydrogen is very light.  Indeed, the weight of the hydrogen you store will be only a very small fraction of the weight of the tanks you have to store it in.

You can choose from various different sizes and strengths of gas tanks.  They can weigh as much as 300 lbs each (for a typical ultra high-pressure steel ‘6K’ tank with a 42.48L storage capacity) and can store hydrogen at pressures of up to 10,000 psi (700 Bar).  At 700 Bar, you are storing just under 38 gm of Hydrogen per liter of tank space, at 200 Bar, you are storing about 14 gm per liter (and about 7 gm/L at 100 Bar).  In addition to heavy bulky steel ‘bottles’ (sometimes with side walls an inch thick) there are more modern containers with high tensile carbon fibres wrapped around the inner bottle, allowing for smaller lighter containers with the same strength as steel.

We prefer medium rather than ultra high pressures – less energy is required to compress the hydrogen to store it and there is less risk of tanks exploding and less stress on adapters and intermediate pressure regulators.  On the other hand, the less the compression, the greater the number of tanks you need.

A possible compromise would be tanks weighing about 150lb each and holding about 7250 liters of hydrogen.  Each of these tanks has enough hydrogen for about 9 kWh of electricity, and costs in the order of $400.  Depending on your perspective, that’s either a lot, or very little.  To put it in perspective, a 12 kWh storage battery, that would be suitable for about 9 kWh of actual power, costs $3000.  So the cost of tanks to store hydrogen is massively less than the cost of batteries, and furthermore, whereas batteries have a finite life and need ongoing trickle charging to maintain their charge, once you’ve filled your gas bottle full of hydrogen, you can pretty much forget about it for a long time into the future.  And you could empty and refill it very many times before it became unreliable (even though we don’t anticipate you doing this much more than once or twice a year).

A suitable compressor is likely to cost in the order of $5000.  Add another thousand or two for miscellaneous piping, regulators, and other incidentals.

In addition to storing compressed hydrogen, it is also possible to store it mixed in with other chemicals (metallic hydrides), or in liquid form.  The former method is complicated but allows for dense storage of hydrogen, the latter method is massively more ‘costly’ in terms of energy needed to liquify and cool it.  We like the simplicity of just compressing the gas.  Less to go wrong, which has to be a major consideration when planning for any sort of emergency backup scenario.

Is Hydrogen Dangerous?

Talking about things going wrong, some people are unnecessarily alarmed at the thought of storing hydrogen.  They have this mental image of the airship Hindenburg in flames, and that colors their perception of hydrogen as a safe fuel.

In actual fact, the most spectacular part of the Hindenburg’s fire and demise was not the hydrogen burning, at all.  It was the very reactive and flammable outside skin of the airship, and also the diesel fuel stored on board.  Yes, the hydrogen did burn, but quickly and relatively harmlessly compared to these other two fire sources.  The Hindenburg would have burned almost identically even if it was full of ‘safe’ helium (the fire is believed to have been started by lightning igniting its outside skin).

Hydrogen is actually less flammable than regular petrol.  Gasoline will burn when it reaches a temperature of 536°F, hydrogen requires a higher temperature of 932°F.

The best thing about hydrogen is that it is very much lighter than air (about 15 times lighter).  If any hydrogen ‘spills’ or leaks or otherwise escapes, it simply shoots upwards, like a cork held at the bottom of a tub of water and then released.  As long as the release of hydrogen is either outdoors or in a structure with venting that allows the lighter than air hydrogen to escape to the outside atmosphere, there will be no problem.

3.  Fuel Cells

Fuel cells have a lot going for them.

They are easily twice as efficient than internal combustion engines, because they directly ‘convert’ hydrogen to electricity, whereas an internal combustion engine converts hydrogen (or any other fuel) first to heat and then to mechanical energy and then from that to electrical energy (that’s three conversions instead of one, each with issues and inefficiencies).

They are quiet, compact, and have no moving parts, making them potentially very reliable.  Indeed, these fuel cells talk about needing maintenance only once every five years.  On the other hand, there is a wide variation in cells as between ones designed for occasional/intermittent/light use, and those designed for heavy-duty ongoing use, and we sense that many fuel cells are still only one or two steps away from experimental and possibly not yet ready for a long hard life ‘in the field’.

It seems that fuel cells commonly consume about 800 liters of hydrogen per kWh of power generated.  Some can go down to the low/mid 700s, and we’ve seen others climb up over 1000 L/kWh.  Compare that to creating 150 liters of hydrogen per kWh of power consumed, and you’ll see that you are getting little more than one sixth of the power back that you used in the first place.

Furthermore, you need to allow for minor other power losses in the total process from solar cell to hydrogen to fuel cell to a/c power in your retreat.  For example, these efficiency ratings are the best possible, assuming the units are running in their ‘sweet spot’ – if you reduce their loads, then their efficiency may drop off.

No allowance is included for the energy cost to compress the hydrogen, for any leaks and losses during transporting the hydrogen from electrolyzer to fuel cell and storing it, nor is any allowance included for other things like energy for cooling systems, and other inputs such as electrolyte and coolant.  We’re also not allowing for more energy loss when the DC power out of the fuel cell is converted to AC power.

Here are some fuel cell systems and their prices.  Here’s another one, slightly less efficient.

Hydrogen Storage – Costs, Costs, and Benefits

So, to summarize, it seems that a hydrogen storage system will cost you in excess of $40,000 for a hydrolizer, another $20,000 for a fuel cell, and let’s say $40,000 for compressors, storage tanks, and everything else.  In other words, you have about a $100,000 cost to get a reasonably sized system established.

This is expensive, and it is also inefficient – you get back about 1 kWh for every five or six you use in the first place, and you’re using a system that can only use power at a rate of about 6.7kW; you’d need to add another $40,000 to your installation cost to be able to recover power at twice the rate.  On the other hand, does efficiency really matter if the energy is otherwise being wasted?

The 6.7kW rate is interesting, it coincidentally means that for every hour you are capturing energy at this rate, you get a net of about 1 kWh of energy for reuse in the future.  Let’s say that in the summer, you have four hours of ‘bonus’ power each day for 150 days, that means you’ve managed to harvest a usable 600 kWh of energy to use during the winter.

That’s actually not as insignificant or disappointing an outcome as you might at first think.

You would need almost 500,000 liters of hydrogen stored in this example so as to get the 600 kWh of output (or, if you prefer, 40 kg).  On the basis of tanks weighing about 150lb each and holding about 7250 liters of hydrogen, this would be a tank farm of about 70 tanks.  Compare that to a comparable battery setup with a similar number of batteries – there’s probably not a huge difference in size (and, in case it matters, the batteries are heavier).  The big difference is in total system cost.  Whereas the hydrogen system has a high cost to get started, it has a low variable cost as you increase its storage.  The battery system has a low-cost to get started, and a high variable cost for each extra battery.  You’re looking at the better part of a $250,000 system to store the same amount of power in batteries as you could with a $100,000 hydrogen system.

So, yes, a $100,000 investment would get you a setup that could store 600 kWh of energy.  Add another $40,000 for more hydrogen generation capability, and more for additional storage as your budget would stretch – perhaps another $80,000 to have 1.2 MWh of energy that is stored over the summer and available over the winter ($180,000 for hydrogen compared to perhaps $450,000 for batteries).  Now the benefits of a hydrogen system start to become very apparent.

There’s another point in favor of hydrogen storage too.  If you were to have an enormous 600 kWh battery storage resource, you might find it ‘costing’ you as much as 6 kWh a day, every day, in trickle charging, to keep the batteries maintained and in good condition.  That’s not a problem in summer, hopefully, but in winter, that is power you can ill afford.  To put that in perspective, you want your 600 kWh of power to last you for 150 days of winter, but during those 150 days, you’ll need 900 kWh of power just to maintain the batteries.  That doesn’t work, does it!

Batteries are the best solution for storing relatively moderate amounts of energy for relatively short periods of time – a day or two up to a week or two.  But for large amounts of energy, and longer periods of time, they start to become less appropriate, as we just saw in the above example.

One further comment.  If we were to invest in a hydrogen system, we would definitely want to make sure we had redundancy – both plenty of spares and ideally two hydrolyzers and two fuel cells.  So either buy two smaller units, or increase your investment still further by having additional larger units as part of the system.

UPDATE March 2018 :  Costs for battery storage have dropped, and probably now using a Li-ion bank of batteries would allow for lower trickle charging needs too.  Without redoing the math, we do note that all major commercial installations for storing surplus energy seem to be moving to battery solutions rather than hydrogen solutions.

Battery technology has improved substantially in the four years since this was written, and promises to continue improving, with the potential for major stunning breakthroughs at any time.  On the other hand, hydrogen and fuel cell technology is more mature and is limited by inviolable physical and chemical constraints that mean there is no perceived potential for similar improvements in hydrogen technology.  We suspect that hydrogen as a way of storing/banking electricity is a technology that has come and gone, never to return.


If you want to store less than, say, 100 kWh of energy, and for a relatively short amount of time (say, less than a month), then probably batteries are your best choice.  But for large amounts of energy storage – indeed, for almost unlimited amounts, and for long-term storage, a hydrogen based storage system comes into its own.

If you’re seriously considering such a system, check the current pricing and the best models out there.  Our sense is that values and capacities are slowly evolving and improving, making the appeal of these systems become greater and greater over time.